The invention is directed to a method for outputting signals from at least one subarea of auxiliary signals and for inputting new or modified signals into at least one free of freed up subarea of transport modules of a synchronous digital signal hierarchy according to the CCITT Draft Recommendations G.70X, G.70Y and G.70Z, in accord wherewith the frame of the transport modules is composed of 9 rows and N-times 270 columns (N is a whole number) for respectively one byte per row and column and contains an administration unit for the acceptance of virtual containers whose frame start is marked by pointers.
Standardized bit rates between 64 kbit/s and 139 264 kbit/s are listed in the "CCITT Red Book", Vol. III-Fascicle III.3, Digital Networks-Transmission Systems and Multiplexing Equipment, Geneva, 1985, page 41.
The periodical "Telecommunications", March 1988, pages 63, 65 and 66 describes synchronous digital signal hierarchies for international use that are known under the designations SONET (synchronous optical network) and NNI (network node interface).
The afore-mentioned CCITT Draft Recommendations contain NNI definitions. Digital signals having a bit rate of 155 520 kbit/s are transmitted in the lowest hierarchy level. Their pulse frame is referred to as a synchronous transport module STM-1. The next hierarchy level is intended for the four-fold bit rate 622 080 kbit/s and synchronous transport modules STM-4. Synchronous transport modules STM-8, STM-12 and STM-16 are possible. In addition to the useful signals, auxiliary signals such as section overhead, path overhead, pointer and fixed stuff bits are contained in these transport modules.
The publication "GLOBECOM'85 IEEE, Global Telecommunications Conference, Conference Record Volume 3 of 3, New Orleans, La., 2 through 5 December 1985, pages 1443 through 1450, particularly FIG. 11, discloses an add drop multiplexer. This serves the purpose of multiplexing STS signals and also serves the purpose of outputting STS-1 signals from incoming STS-N signals of a higher hierarchy level. STS signals are composed of pulse frame having a header for auxiliary signals and of a main part for signals to be transported that can in turn themselves contain auxiliary signals in the form of a path overhead. An inputting and outputting of auxiliary signals or subareas thereof is not provided.
U.S. Pat. No. 4,574,375, finally, discloses a an interface arrangement for a telephone system or the like. In this, complete digital signals incoming on a bus line have their channel nested in a pulse frame taken for a processing such as setting signal level, dual tone multi-frequency signaling or network echo elimination and are subsequently returned onto a bus line. Here, too, neither auxiliary signals nor subareas thereof are separately input or output.